Step Height Standards Research Articles

Traceable methods for vertical scale characterization of dynamic stroboscopic scanning white-light interferometer measurements.

Stroboscopic scanning white-light interferometry (SSWLI) can be used for 3D imaging of oscillating samples. It allows measurement of micrometer to millimeter size samples with nanometer vertical precision. Unlike coherent light source systems the SSWLI can measure unambiguously samples with vertical steps. Traceability of the vertical displacement measurement is important with SSWLI since the height measurement is not related to any specific monochromatic light wavelength. For static measurements SSWLI can be calibrated using, e.g., step height standards, but to characterize dynamic measurements traceable samples with accurate motion are needed due to error sources related to the frequency response of the SSWLI. In the presented method, SSWLI measurements are performed on dynamic transfer standards, which are characterized using a laser interferometer traceable to the SI meter. In this work dynamic SSWLI measurements at subkilohertz to 10.7kHz frequencies with micrometer range displacement are characterized. The expanded uncertainty (k=2) was 9.6nm for a measured displacement of 766nm at 10.7kHz. The methodology can be used up to the frequency limits of the SSWLI using suitable samples.

Study on Spatial Frequency Domain Algorithm and White Light Interference System Based on NMM

White light interference technique for topography measurement effectively avoids phase ambiguity in phase-shifting interferometry. The spatial frequency domain algorithm based on scanning white light interference technique has the advantage of insensitivity to noise and higher calculation accuracy compared with other methods. The white light interference sensor is constructed based on nano positioning and nano measuring machine (NMM), the calibrated step height standard of 100±3nm is measured. The spatial frequency domain algorithm is adopted for data processing, the repetitive test result of 97.9nm and standard deviation of 0.48nm are achieved. To verify the measuring ability of complex device, the number ‘242’ on ink box is measured and three-dimensional reconstruction is conducted. The high precision and traceable measurements of micro/nano scale step height standard and complex devices are realized by the white light interference system based on NMM with steady frequency laser interferometer built-in.

Imaging interference microscope for nanometrology

Here we report the development of the primary nanometrology capacity at the National Metrology Institute of Brazil (INMETRO). An interference microscope of the Linnik type has been developed and subjected to optimization and characterization studies. The recording of the fringes is done by an automated CCD system with 2 possible processing approaches: interferometric pattern processing and the phase stepping technique. Current progress in the development of the hardware and software adequate for sub- nanometer resolution of the instrument is reported. A study of systematical errors of the interference microscope has been performed. The instrument is aimed for international key comparisons of step height standards.

Measurement of Step Height Using White Light Spectral Interferometry

The development of micro-nanomanufacturing technology leads to higher requirement for measurement technology, which gives birth to the ultra-precision measurement technology. As a kind of low coherence interferometry technology, spectral interferometry has been proposed. In this paper, the theory and system of white light spectral interferometry were described in detail, and the measurement principle of micro-structure was analyzed. The spectral interference signal was recorded and the phase information was retrieved from it by using five-step phase shifting algorithm, which includes the phase change on reflection from the stucture. So the optical path difference (OPD) can be obtained, which represents the height information. Three methods including slope method, single wavelength method and least square method were discussed based on the theory deduction and the experimental analysis. A step height standard was measured and the results show that this method has a good accuracy.

Improving axial resolution in spectral domain low-coherence interferometry through fast Fourier transform harmonic artifacts

Low-coherence interferometric setups in the Fourier domain can experience false structures after the Fourier transform procedure due to signal saturation; in fact, these structures are located at multiple frequencies of the original signal, also referred to as harmonics. This study aids in a better understanding of this phenomenon. The aim of the present work was to show that these features can be used to improve differential axial resolution in highly reflective samples. Using an optical coherence tomography system and calibrated step height standards, it was possible to achieve a resolution greater than the light source coherence length.

Study on Phase Shifting Algorithm and System of White Light Interference

The white-light interferometry (WLI) has been widely used in 3D topography measurement. This paper introduces a white light phase shifting method for interferometry with the combination of Hariharan phase shifting and WLI. A micro/nanolevel mechanic system was designed and built for the experiments. To verify system accuracy and feasibility, a 100nm step height standard was measured by the designed system and the metrological nanomeasurement machine (NMM). Results of 102.7nm and 102.5nm are obtained respectively. En value of 0.14 is calculated, demonstrating the reliability of result measured by the system. Based on classic nanoquantity traceability system, the measurement results can effectively traced back to the definition of nanometer magnitude, which can improve the accuracy of measurement.

Dimensional metrology in the macroscopic range with sub-nanometre resolution

Nanomeasuring machines are devices for solving various positioning and measuring problems in a range of several millimetres with sub-nanometre resolution. These devices are used for positioning, probing and measurements. The combination of this machine with a scanning force microscope leads to improved quality in the calibration of standards. The measurement accuracy and stability of the scanning force microscope are important for the achievable measurement uncertainty. Many systems are influenced by the creep, hysteresis and bending of the included piezo actuators. A scanning force microscope head with a combined deflection detection system that comprises an interferometer and a beam deflection system was developed. Due to this system, it is possible to simultaneously measure the displacement, bending and torsion of the cantilever with only one focussed beam. An additional high-speed piezoelectric actuator for the vertical motion of the cantilever was integrated and is controlled by the bending signal. The outcome of this additional control system is a much higher scan speed. The interferometer system can be used for precise measurement of the vertical cantilever motion. Hence, non-linearity and hysteresis in the actuator do not affect the measurement. The device was used for several calibration measurements on step height and lateral standards. This article deals with the set-up, function and application of a scanning force microscope head for dimensional metrology with the nanomeasuring machines.

Research on Characterization Methods of Nano Dimension Standards

This paper develops one method to characterize nano dimension standards using Scanning White Light Interference Sensor (SWLIS) based on Nano Measurement Machine (NMM). The experimental results show the average value of SHS8-440 low step height standard is 44.15 nm and SHS8-100.0 high step height standard is 100.29 μm, with a standard deviation of 0.30 nm and 0.03 μm, respectively. Also, SWLIS is performed to measure and characterize step height standards, which cover most of the conventional step height standards produced by VLSI Standards Incorporated (VLSI). Additionally, atomic force microscope (AFM) is used as a beneficial supplement due to low lateral resolution of optical methods. The average value of TGZ1_PTB 1D grating from NT-MDT Company is 3000.2 nm with a standard deviation of 0.3 nm by AFM.

Final report on APMP.L-K8: International comparison of surface roughness

Surface roughness calibration services of 16 countries from four metrology regions are compared through measurements of roughness and step height standards. The artefacts circulated include three steps of nominal depths 0.4 µm, 2.4 µm and 10 µm, whereas the roughness sections of both type C and type D profiles have nominal Ra values of 0.2 µm, 0.95 µm, 1.5 µm and 3.1 µm. Two soft-gauges were also circulated for comparison of software independent of hardware. For the steps, parameter d is reported, while for the type C and type D standards and soft-gauges, 14 different roughness parameters are reported between them. Concluding measurements from the pilot in general show good standard stability; however, for some parameters on the artefacts of larger roughness, stability may be considered less certain and this may be an issue in additional outliers in results from the last few laboratories in the schedule. For each parameter, a key comparison reference value (KCRV) is determined using a weighted mean with outliers excluded based on the Birge ratio method until all accepted values form a statistically consistent population. For the five artefacts, out of 35 separate parameters, only ten have good agreement of all submitted results. Where some parameters had to be excluded from the KCRV, some laboratories had consistent problems with particular types of parameter over the different artefacts, while for other laboratories the types of parameters excluded seemed to be random. Comparison of soft-gauge results and artefact results has proven to be inconclusive.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Measurement strategies and uncertainty estimations for pitch and step height calibrations by metrological atomic force microscope

Gratings and step height standards are useful transfer standards for lateral and vertical length scale calibration of atomic force microscopes (AFMs). In order to have traceability to the SI-meter, the standards must have been calibrated prior to use. Metrological AFMs (MAFMs) with online laser interferometric position measurements are versatile instruments for the calibrations. The developed task-specific measurement strategies for step height and pitch calibrations with the Centre for Metrology and Accreditation's (MIKES's) metrological AFM are described. The strategies were developed to give high accuracy and to reduce measurement time. Detailed uncertainty estimations for step height and grating pitch calibrations are also given. Standard uncertainties are 0.016 and 0.018 nm for 300 and 700 nm pitch standards, respectively, and 0.21 and 0.44 nm for 7 and 1000 nm step height standards.

Novel control scheme for a high-speed metrological scanning probe microscope

Some time ago, an interferometer-based metrological scanning probe microscope (SPM) was developed at the Institute of Process Measurement and Sensor Technology of the Ilmenau University of Technology, Germany. The specialty of this SPM is the combined deflection detection system that comprises an interferometer and a beam deflection. Due to this system it is possible to simultaneously measure the displacement, bending and torsion of the probe (cantilever). The SPM is integrated into a nanopositioning and nanomeasuring machine (NPM machine) and allows measurements with a resolution of 0.1 nm over a range of 25 mm × 25 mm × 5 mm. Excellent results were achieved for measurements of calibrated step height and lateral standards and these results are comparable to the calibration values from the Physikalisch-Technische Bundesanstalt (PTB) (Dorozhovets N et al 2007 Proc. SPIE 6616 661624–1–7). The disadvantage was a low attainable scanning speed and accordingly large expenditure of time. Control dynamics and scanning speed are limited because of the high masses of the stage and corner mirror of the machine. For the vertical axis an additional high-speed piezoelectric drive is integrated in the SPM in order to increase the measuring dynamics. The movement of the piezoelectric drive is controlled and traceable measured by the interferometer. Hence, nonlinearity and hysteresis in the actuator do not affect the measurement. The outcome of this is an improvement of the bending control of the cantilever and much higher scan speeds of up to 200 µm s−1.

Uncertainty contribution of tip-sample angle to AFM lateral measurements

AFM measurements are very important for quality control in the photovoltaic, microfluidic, electronic or micro-optic industries. This work proposes an algorithm to complete the uncertainty evaluation of AFM systems along the XY -axis under conditions where tolerance of curved surfaces must be controlled. This algorithm is also tested for tilt angles between tip and sample from 0° to 9° using an experimental arrangement which consists of an AFM instrumented with an inclinometer and four step height standards. Results show good agreement between the theoretical model and experimental results for samples with larger steps TGZ03 (465 nm) and TGZ11 (1416 nm), but with poor results for the smaller samples TGZ01 (17.6 nm) and TGZ02 (73.1 nm). An angle of 9° shows an error of about 3% in the horizontal determination of the step dimension, but it could increase to 47% for a tilt angle of 30° according to the theoretical model. The angle error between tip and sample is included in the uncertainty budget using a uniform distribution. An evaluation is performed in a theoretical rolling machine for imprint lithography where a step must be measured with nominal dimensions of 3 μm— X -axis and 1 μm— Z -axis. An assumed tip-sample angle is assumed that changes from 0° to 22.5° (curved form) and produces an uncertainty contribution to the X measurement of 55.7 nm. This uncertainty is important and must be considered to guarantee tolerances in quality control of curved form products.

Measurements of dimensional standards and etalons with feature size from tens of micrometres to millimetres by using sensor strengthened nanomeasuring machine

A laser focus sensor and a contact inductive sensor have been coupled to an ultra high precision positioning stage, referred to as a nanomeasuring machine (NMM), for measurements of dimensional standards with a large measurement volume of 25 mm × 25 mm × 5 mm. Control and measurement software have been designed and complemented. The measurement uncertainty of strengthened NMM has been analyzed and discussed. Groove depth and step height standards with feature heights of tens of micrometres to millimetres as well as aspherical surface etalons are calibrated by nanomeasuring machine. The paper also introduces a method for characterising the measured aspheric surface by least square fitting the measured data to a quadratic paraboloid function. The obtained quadratic coefficients are compared to that measured by a conventional coordinate measuring machine (CMM) and a stylus profiler, showing a good agreement.

Final report on EUROMET.L-S15.a (EUROMET Project 925): Intercomparison on step height standards and 1D gratings

Measurements have been made at five national metrology institutes (NMIs) in the subject field of dimensional measurement using scanning probe microscopy. Four of the participating NMIs are in Europe, the fifth is in the Asia-Pacific region. Each NMI made measurements of four step height standards and two 1D grating standards. These are typical artefact standards used for dimensional nanometrology. Each participant used a different atomic force microscope to perform the measurements. The report lists the results obtained by the individual participants, as well as an analysis of the results and their uncertainties, based on calculation of the weighted means and En values. The results are in good agreement with one another.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Traceable Nano Geometric Structure Measurement and International Comparison

The accuracy of geometric structure plays a key role to guarantee high quality of the nano function device and electronic device. In June 1998, the Consultative Committee for Length (CCL) of International Committee for Weights and Measures decided to carry out international comparisons of five different types of artifacts: Step height standards, 1D-gratings, line scales, 2D-gratings and line width standards. The paper described the activity of NIM in the international comparison measurement of first three items, include the characters of artifacts, the working principle of instruments, the measuring procedures, the calculation methods, the comparison results and the measurement uncertainty.

A new method for the calibration of the vertical scale of a stylus profilometer using multiple delta-layer films

A new method for the vertical scale calibration in step height measurement has been established using a multiple delta-layer film. The vertical scale of a stylus profilometer can be traceable to the length unit by the certified film thickness in a multiple delta-layer. A Si/Ge multiple delta-layer film with six Si layers separated by Ge delta-layers was developed. The total thickness and delta-layer spacing were certified by high resolution transmission electron microscopy. Six craters with different depth were formed on the Si/Ge multiple delta-layer film by ion beam sputtering via SIMS depth profiling. The depths of the craters can be determined from the certified depth of the delta-layer and direct measurements using a stylus profilometer calibrated by a step-height standard. The vertical scale of a stylus profilometer can be calibrated by the slope and the offset of the measured crater depth fitted as a function of the certified nominal thickness.

Detecting and addressing the surface following errors in the calibration of step heights by atomic force microscopy

Step height standards are widely used for the calibration of the z-axis scale of scanning probe microscopes. NPL, in common with a number of other national measurement institutes, has constructed a metrological atomic force microscope (MAFM) that delivers traceable calibration of step height standards. The measurement uncertainty of the calibrations is a combination of those uncertainties associated with the metrology frame, whose values can be estimated with good accuracy, and those associated with the AFM head, whose values are more difficult to quantify. Estimates of these values are usually based on the repeatability of measurements, either in isolation for a particular sample, or in combination with historical data on instrument performance. That the estimates are reasonable may be verified by comparing the AFM measurements with measurements made on other independent, traceable systems. This paper describes how the verification process led to the detection of a significant following error in one of the heads employed on the NPL MAFM, which could then be evaluated and addressed. The value of measurement uncertainty for the step height measurements is also dependent on the physical characteristics of the standard. Results are presented for measurements of a fine scale step height standard that has been designed for optimum compatibility with the measurement procedure in order to reduce the measurement uncertainty.

A comparative approach for calibration of the depth measuring system in a nanoindentation instrument

Within the past decade, the nanoindentation method has developed into an indispensable tool of quality assurance enabling determination of the mechanical properties of small volumes of material. For a high quality of the characterisation of these materials the calibration of nanoindentation instruments, particularly their depth measuring system, is necessary. A comparative approach is presented to fulfil the calibration requirement, in which an optical probe interferometer and step height standards are used. In order to improve the measurement uncertainty of the calibration procedure based on step height standards, a simple force modulation technique was introduced. Experimental results indicate that the two calibration methods coincide. Therefore advice on how to choose a suitable calibration method is given.

International comparison of surface roughness and step height (depth)standards, SIML-S2 (SIM 4.8)

Calibration services of five countries from the Sistema Interamericano de Metrología (SIM) region are compared through measurements of surface roughness and step height standards. A surface roughness standard with a nominal roughness average (Ra) value of 0.2 µm, a surface roughness standard with a nominal Ra value of 3 µm and a nominal spatial wavelength of 99 µm, and three step height standards with nominal values of 2.55 µm, 0.38 µm and 0.03 µm are compared. Special attention is paid to the influence of the long wavelength cut-off ratio of the measurements. Results are reported for Ra, maximum height of profile Rz, mean width of profile elements RSm, and step height d, depending on the sample measured. The initial reported results show that the laboratories agree on all of the measurements within their stated and published uncertainties. Observations are then discussed about the definition of Rz, the effect of instrument noise on Rz, the different step height parameters d and Pt, differences between the laboratories in reporting Type A statistical uncertainties, the method for calculating the uncertainty of the reference value, and the importance of accounting for correlations between the reference value and individual lab values when calculating the degrees of equivalence. After corrections and reanalysis the laboratories still agree well considering their stated uncertainties.Main text. To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the SIM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

314 マルチボールカンチレバーのナノ計測特性(OS-10 加工計測・評価)

For measuring the surface profile of soft thin films such as photoresists we proposed the method using multiple ball cantilevers and constructed a multi-ball-cantilever AFM system, which covers a wide area at high speed. Each cantilever has a ball stylus with a diameter that dose not plastically deform measured surfaces. In this research, to realize high accuracy in measurement, we observed the behavior of the multi-ball-cantilever using the white light interferometer. We discussed the nano measurement characteristics of the multi-ball-cantilever by measuring the step height standard.